Selector circuit



Feb. 26, 1935. L RQTTER 1,992,445

SELECTOR CIRCUIT Filed April 14, 1952 d, [RpTER BY H ATTORNEY Patented Feb. 26, 1935 UNITED STATES SELECTOR Laszlo Rotter, Berlin, Germany, assignor, to Radio I Corporation of America, acorpdra'tion of Dela- V ware Application April 14, 1932, Serial No} 605,196

' In Germany April 23, 1931 2 Claims. (01. 250-i This invention has for its object to provide a device permitting of the selectivity of a wireless receiving set being increased and suppressing the disturbances which may arise owing to the wave- 5 lengths to which the various broadcasting stations are tuned being very close to each other. For this purpose the device comprises a tuned circuit by which onlya narrow frequency band is transmitted. In addition, the device is so constructed as to enable it to be coupled in various ways to the antenna and to the receiving set so that in anyparticular case always that connection can be chosen which gives the most favour able results.

The most favourable way of connecting an antenna to a receiving set is intimately connected with the properties of this set. Thus, for example, it is desirable that the amplification by the receiving set should be identical as nearly as possible for any frequency. In case therefore of an amplifier amplifying high frequencies to a greater extent than low frequencies, preferably a coupling will be used which is stronger. in the case of low than of high frequencies, whereas'if conversely high frequencies are less satisfactorily amplified by the amplifier a coupling will be chosen which increases at higher frequencies.

In addition, the properties of the antenna" and also the wave-length to be received influence the choice of the way of coupling. Thus, for example, if an inductive antenna coupling is used, the choice of the inductance coil connected in series with the antenna will depend on the length of the antenna. If feeble signals are to be received, generally a direct antenna coupling will be used, a small condenser being, if necessary, interconnected between the tuned circuit and the antenna in order to reduce the infiuence of the antenna capacity on the tuning of this circuit.

The device according to the invention combines all these connecting possibilities. It comprises two series connected inductance coils and in parallel therewith .two series connected condensers one of which is variable, and also a coil coupled to one of the inductance coils, connecting terminals for connection to an antenna being provided on each of the coupled coils (if necessary with the interposition of a small condenser) and both the third coil and the fixed condenser being furnished with connecting terminals for connection to a receiving set.

Among the two coils included in the tuned circuit, the antenna coil comprises a considerably greater number of turns than the coil to be used for connection to the receiving set. These two coils are so arranged that their magnetic fields cannot influence each other. For this purpose, for example, the small coil is arranged within. the large coil, their axes being normalto each other.

In order to avoid any interference by external fields, the said coils and condensers are housed in a preferably cylindrical casing. The carrier of the coil serves also as a means of attachment for thevariable condenser to be used. The metal casing should be sumciently distant from the coil turns so that eddy current losses are prevented. In addition, the casing may be slotted so as to avoid'the production of closed circuits for the induced currents. The assembling of the electric parts to form a closed unit has the advantage of a simple mounting and a cheap manufacture. The base plate of the metal casing may be so constructed as to permit of the casing being readily built together with the receiving set to be used so that after the mounting aunitary piece is formed.

In order that the invention may be clearly understood and readily carried into effect one embodiment thereof will now be described more fully with referenceto the accompanying drawing, in which Figure 1 shows the embodiment referred to, and

Figure 2 is a diagram of connections of the selection circuit. v I

An antenna 1 may be connected to an antenna coil 2 which is earthedat 3. The coil 2 is coupled to a large coupling coil 4 of the selection circuit and is mounted therewith on the same cylindrical carrier5. Internal of the carrier-'5 is a small coupling coil '7 mounted on a further carrier 6. The oscillatory circuit includes in addition a rotary condenser 8 and a fixed condenser 9. The receiving set may be connected to terminals 10 and 11; The means of connection are evidently not limited to terminals or bushes but the connection may be eifected in any suitable manner. The coil carrier 5 is secured to the lid 12 of the metal 'case 13 and carries at itsother end by .means of a bail 14. a rotary condenser 15 the spindle of which extends across the wall of the casing 13 and is provided with an adjusting knob 16.

It is, of course, obvious that the invention is not limited to the embodiment illustrated but is applicable to various other forms of construction.

WhatIclaimis: v

1 A coupler adaptedto be connected between an antenna and a radio receiver comprising, a primary coil provided with taps for connection to the antenna circuit and ground, a secondary ciri tune the' secondarypircuit to any desired frecuit comprising a secondary coil coupled to the primary coil and an auxiliary coil in series with the secondary coil said last two coils being mounted so that their respective axes are normal to avoid coupling between them and a pair of condensers in series shunted across said two series connected coils, one of said condensers being variable so as to provide a tuning element to quency of a predetermined frequency range, output taps on said auxiliary coil to provide a connection toia radio receiver input and output taps across one of said condensers for providing an additional connection to a radio receiving input if desired, an antenna connection terminal and means including a coupling capacity for connectadapted to support the second coil, the second coil being wound around the second carrier so that its axis is at right angles to the axis of the first coil, and means for mounting the variable condenser between said yoke and the housing.

LASZLO RO'I'IER. 

